The recycling and transformation of waste paper materials into secondary paper products is important from an environmental standpoint as well as an economical one. Not only does it save natural resources and reduce volumes of trash and pollution, but if carried out in an efficient manner, utilizes an inexpensive source of paper filler. However, a number of problems must be overcome in the successful transformation of waste paper materials to secondary paper of suitable quality and performance.
The secondary fiber industry utilizes waste paper or paper products as a source of paper fiber (commonly referred to as "secondary fiber") to produce finished paper products. Waste paper and paper products that are the source of the secondary fiber include any waste paper materials such as newspapers, books magazines, waste bags and boxes, mixed office waste, computer printout, ledger, etc. The once-processed papers contains various types of adhesives (pressure sensitive, hot melts, etc.), inks, and coating binders. An extensive list of natural and synthetic adhesives found in different grades of paper is described in the article, "Stickies Control by Detackification", Robert D. Moreland, 1986 Pulping Conference, pp. 193-196. This article also describes in some detail the problem solved by the present invention.
Different adhesive materials as well as pitch are present in paper fiber furnishes and a particular problem in paper recycling is the presence of adhesives, ink and coating binders (primarily those composed of synthetic polymers) that are found on some of the waste paper being utilized. More specifically, labels, decals, stickers, stamps, envelopes, book bindings, etc., each have adhesives associated therewith and these must be removed when the waste products are recycled. These adhesive contaminants, known in the trade as "stickies and tackies" cause numerous problems, both in terms of process and product performance. Some of the commonly used adhesive materials include, for example, styrene butadiene rubber, vinyl acrylate, polyvinyl alcohol, natural rubber, isoprene polystyrene, polypropylene, ethylene vinyl acetate and the like.
In papermaking, pitch is present in the form of a mixture of calcium carbonate, calcium soaps from wood components and other miscellaneous residues. A tacky, viscous substance, it is used extensively in the papermaking process and in the past has been extremely difficult to remove.
Specifically, the contaminants deposit on and adhere to machine surfaces throughout the paper processing machine thereby disrupting operations. They can fill or plug forming fabrics and press felts. The stickies will also mark or hole the paper sheet. If the contaminants are present in the paper, they will cause sheet defects or spots. This results in poor visual aesthetics of the paper, and poor surface properties can result in printing difficulties. The tackiness of these contaminants may also cause adjacent sheets, when wound in roll form, to adhere to one another. This can cause tears, breaks and holes in the converting processes.
Since stickies generally have the same density as water and fiber, they are difficult to remove. The stickies may be pliable and therefore cannot be completely screened from the water and/or fiber mixture. Equipment currently being utilized is effective to a certain degree but not 100%.
Obviously, production economics are affected quite severely when stickies-related problems are encountered. Stickies commonly necessitate complete shutdown of the manufacturing equipment in order to remove such by solvent washing techniques. The cleaning process is expensive due to downtime as well as solvent costs.
To deal with the problem of stickies and tackies, a number of strategies have been employed by papermakers. These strategies include mechanical and chemical means to either remove or passivate the contaminants.
Mechanical means of removing the contaminants include slotted pressure screens, hydrocyclones, and cleaners of various types. Also, thermal/mechanical dispersion units are employed to break the contaminants into micron sized particles, which are then difficult to detect in the final sheet. Despite these techniques, 100% removal of contaminants by mechanical means cannot be accomplished.
Chemically, several approaches are taken, including passivation or detackification of the sticky contaminant surfaces. Such detackification agents, include inorganic materials such as talc and zirconium compounds, organic materials such as polyvinyl alcohol, and hydrophobic synthetic fibers such as polypropylene. In addition, various dispersants may be used to prevent the contaminants from agglomerating. The small dispersed contaminants may be fixed to the paper sheet by the use of cationic polymers. Finally, if the contaminant problem becomes severe, solvents will be used to wash and remove the materials from the machine clothing.
The present invention relates to a method of detackifying secondary fiber paper pulps by treating the pulps with a hydrophobically modified guar and sodium acrylic-maleic acid copolymers.
U.S. Pat. No. 5,415,739 to Furman et al. discloses a process for the detackification of adhesive contaminants in secondary fiber paper pulps using a water soluble terphthalate glycol terpolymer. The terpolymer is prepared as the distillation product of polyethylene glycol monomers comprising at least 80% of the terpolymer; a phthalic ester moiety and a simple glycol such as ethylene glycol, propylene glycol and the like. The terpolymer is either added directly to the furnish prior to sheet formation or is sprayed on afterwards in the shower water used to clean off the fabrics and felts employed during sheet formation and dewatering.
U.S. Pat. No. 4,956,051 to Moreland discloses the use of a polyvinyl alcohol polymer to detackify adhesive materials contained in the secondary fibers of recycled waste papers. The polyvinyl alcohol polymer also contains some hydrophobic moieties such as acetate, propionate, butyrate and the like. The compound is added to the water sprays and showers used to wash the felts, wires and press rolls.
U.S. Pat. No. 4,886,575 also to Moreland discloses and claims a method for the detackification of hot melt and/or pressure sensitive adhesive materials contained in a fibrous paper sheet made from waste paper materials using a polyvinyl alcohol polymer that contains at least some hydrophobic groups such as acetate, propionate or butyrate, is 70-99% hydrolyzed and is water-soluble. The polymer is added to the water spray or shower for application to the paper sheets once pressed.
Finally, U.S. Pat. Nos. 4,781,794 and 4,698,133 also to Moreland disclose a method for the prevention of the deposition of adhesive materials contained in the waste paper materials used to make secondary paper products. The process entails the use of lower alkyl derivatives of cellulose in a dilute solution that is applied during the shower rinse of conventional secondary paper manufacturing production lines. Suitable derivatives include water soluble methyl ether derivatives such as methyl cellulose, hydroxypropyl methyl cellulose; hydroxybutyl methyl cellulose and the like. These are nonionic in nature and may also be used to spray the machine rollers and parts.
None of these prior art methods have been able to completely passivate the "stickies" and other contaminants which render the final paper product less than ideal and often times cause substantial defects and flows. It is an object of the present invention then, to provide a superior detackification process for use in the paper industry that prevents substantially all of the adhesive contaminant from depositing on and incorporating into the secondary paper products made from recycled waste materials or virgin pulp. The process is carried out using standard methods known in the art and yet provides a superior product at lower costs.